Gas Blowing Out Of Carburetor

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Gas blowing out of the carburetor is a common problem in all carbureted engines, including mowers. 

If you are currently dealing with the same issue, continue reading.

In this article, I reveal possible reasons why your carburetor might blow out gas and the exact steps to fix them.

Tools Needed For The Job

You will need the following tools and materials:

  • Screwdriver
  • Needle-nose pliers
  • Nut driver
  • Socket Set
  • Gloves
  • Carburetor cleaner
  • Compressed air
  • Test tube or a small olive bottle

Reasons Why Your Carburetor Might Be Blowing Out Gas

Some of the reasons why your mower carburetor might be leaking gas include:

  • Ethanol in fuel
  • Float needle not shutting off gas
  • Primer bulb not filling
  • Disconnected fuel line
  • Worn out carburetor gasket
  • Stuck float
  • Dirty carburetor

Gas Blowing Out Of Carburetor: Possible Causes, Diagnosis, And Fixes

1. Ethanol in fuel

Using fuel that contains ethanol is bad for your carburetor’s health. The mower’s carburetor is not designed to accommodate ethanol. Continually using a high amount of ethanol gas can clog your carburetor or cause the oil line to dry out and harden, which will cause your gas to leak.

Diagnose: Run an ethanol test on every fuel you buy to determine the level of alcohol it contains.

How To Run An Ethanol Test  In Simple Steps

  • Get a test tube or a small olive bottle about six to seven inches.
  • Make a line on the bottle, about two inches above the bottom.
  • Fill water into the bottle up to the line.
  • Fill the rest of the bottle with gas.
  • Cover the bottle, shake it, leave it and let it stand.

The result: If there is ethanol in the gas, it will mix up with the water. Check the line to see if the water level has increased. If the water level increases, the gas contains ethanol and should not be used.

Fix: Avoid using fuel that contains a high level of ethanol.

2. Float Needle Not Shutting Off Gas

The float needle regulates how fuel enters the carburetor by opening and closing the float valve to allow gas to enter the float bowl. 

When the float needle is worn-out or clogged with dirt, it will not be able to regulate fuel inflow into the carburetor. The fuel will continue to flow until it fills the carburetor and it starts to leak.

Diagnose: Remove your carburetor from your mower, locate the float needle and remove it from its seat. Check the tip of the float needle for debris or wear. 

Fix: If dirt is your float needle tip, you can simply clean it off, but if the tip of the float needle has begun to wear, you should change it.

3. Primer bulb not filling

The job of the primer bulb is to draw fuel into the carburetor, but when it’s brittle or not correctly fixed, it might not pump gas into the carburetor but instead cause fuel to leak through it.

Diagnose: Push the primer bulb and see if it pumps gas into the carburetor. If it doesn’t, then it might be the problem.


  • Check the primer bulb’s connection and ensure it connects to the carburetor correctly.
  • Check the primer bulb for wear or dirt.
  • Replace your primer bulb if it’s damaged. Do not try to repair or patch it. 

4. Disconnected Fuel line 

The fuel line or pump transfers fuel from the fuel tank to other parts of an engine, including the carburetor. If the fuel line is disconnected or not correctly connected to the carburetor, it might cause fuel to leak.

Diagnose: Check the connection between the fuel line and carburetor to see if it’s properly connected.

Fix: Connect the fuel line to the carburetor correctly if it’s not properly connected. Note that the fuel line should be on the brass nipple, which is located on the carburetor side.

5. Worn out carburetor gasket

The job of the carburetor gasket is to keep the engine running smoothly by keeping air and oil locked in the carburetor. When the gasket is worn or torn, it causes the carburetor to leak fuel.

Diagnose: If the fuel leak is followed by other symptoms such as backfire,     

engine not accelerating and trouble starting your machine, the carburetor gasket might be the problem.

Fix: If the carburetor gasket is worn, you must replace it.

6. A stuck float

The float regulates the amount of fuel that enters the float bowl. When the float is stuck open, gas will continue to enter the reservoir until it’s full and start to spill.

Diagnose: Aside from gas spilling, a stuck float usually shows symptoms like engine hesitating, engine not idle, and engine misfiring.

Fix: Tap the float firmly with a screwdriver bottom until it unsticks. 

Do not tap the float with a hammer, as it might damage the float.

7. Dirt in the carburetor 

If you have done everything listed above, but your carburetor is still leaking gas, it might indicate that your carburetor is clogged. 

When dirt clogs the carburetor, it will prevent gas from flowing into the engine and might begin to spill fuel.

Diagnose: Engine not starting, poor engine performance, engine running lean or rich, overheating, and backfiring are signs that your carburetor is dirty.

Fix: Thoroughly clean your carburetor.

How To Clean Your Carburetor In Simple Steps

  • Using a screwdriver, remove the air filter to access the carburetor.
  • Using a socket set or the nut driver, remove the carburetor. 
  • Disassemble the carburetor.
  • Using a carburetor cleaner, clean the carburetor and the carburetor parts.
  • Dry the carburetor parts with compressed air or allow them to air dry.
  • Reassemble the carburetor.
  • Mount the carburetor back on the mower
  • Test the mower if it still leaks.

4 Simple Lawn Mower Maintenance Tips For Optimum Performance

You can carry out specific activities to preserve your mower engine and increase its lifespan. They include;

1.  Inspect your mower before use

Perform a quick inspection on your mower before using it at the beginning of a new season. Check for loosened nuts, rot, and disconnected wiring before firing on your mower.

2. Use recommended fuel

The recommended gas for lawn mowers is gas with a minimum of 87 octanes containing up to 10% ethanol. Be careful where you get your fuel, as some fuel stations sell gas with as high as 15% ethanol, which is unsuitable for your mower.

3. Avoid Using stale gas

Do not use gas from the last season at the beginning of the new winter season, as the old gas might become thick and cause problems for your engine. Ensure to start new seasons with fresh and clean oil and gas. 

4. Do a routine check on your engine parts

Whether your mower is in use or not, regularly check on its essential parts like the carburetor, carburetor gasket, gas filler, etc.


Again, Some of the reasons your carburetor might blow out gas include excessive ethanol in your gas, the float needle not shutting off gas, the primer bulb not filling the carburetor, and a stuck float, among others.

Troubleshoot and inspect your carburetor to find the possible causes, and follow the steps provided in this article to fix the problem. However, if the problem persists after following all the steps, you might need to consult a professional repairer.